How can i be sure my program makes use of my video card? should i use ogl extensions to make use of multitexturing, t&l, pixel shading etc.? do u know a better tutorial than nehe''s about that, or can u explain me a bit about that? and if i have a voodo3, do u think it can couse the fog not to work?

Just use glGetString(GL_RENDERER) to know what type of renderer your OpenGL code use.
Anyway if your system use software render, your apps will be REALLY slow.